Hi, Ginala, welcome to the forum.
Open Gmail app
Tap App options button (the circle with three horiz. lines in it, to left of battery indicator)
Accounts
Your account will probably already be listed here, fine if it is or not
Tap "Add Account"
Follow the instructions to re-add your gmail account (that's right you're going to add the same account you already setup once, again). At some point, there should be two checkboxes regarding the syncing of the account, make sure both are checked.
Note that when you're finished with this, you should not have delete your original Gmail account, because only one account will be listed (even after adding the duplicate account).
Things should sync properly now.
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